Download Introduction to plant viruses

Lab Tuesday: Virus Diseases
• Quiz for Bacterial Pathogens lab (pp 67-73) and Biocontrol
of Crown Gall (p. 113-117), Observation of Viral
Movement in Plants (p. 119), and Intro section for Viruses
(pp. 75-77).
• Continue Koch's postulates experiment (re-inoculation step)
• Record data from Race I.D. of Wheat Stem Rust experiment
• Record data from bacterial pathogen HR assay in tobacco
• Observation of Viral Movement in Plants
• Virus lab
• Turn-in ‘Disease of Week’ write-ups.
Introduction to plant
viruses
Valerian Dolja
Cordley Hall 4067
Tel. 737-5472
1898
Dmitriy Ivanovskiy (Russia)
and
Martinus Beijerink
(The Netherlands)
describe The first virus:
Tobacco mosaic virus
Viruses are the major players in the genetic
universe
1 cm3 of seawater contains 106-109 virus particles
Suttle, C.A. (2005) Nature 437:356
There are millions of diverse bacteriophage species
in the water, soil, and gut
Edwards and Rohwer (2005) Nat. Rev. Microbiol. 3:504
Viruses dominate biosphere: there are 10-100
viruses per each living cell
The metagenomes of viruses and cellular organisms
have comparable complexities
VIRUSES
Non-cellular form of life
Obligate intracellular parasites
Exist as inert particles (virions)
outside the cell
Virions harbor viral genome protected
by protein shell
Viral form of life
CELLS
VIRUSES
Reproduction
Binary fission
Assembly from the
pools of components
Membrane
All phases of the
life cycle
Only enveloped viruses
when outside the cell
Translational
machinery
All types of cells
None of the viruses
Genome
dsDNA
ds or ss DNA or RNA
Genetic Diversity
and
Host Ranges of
Viruses
Virus origins from
Precellular
Gene Pool
A phylogenomic view of life
RNA
Bacteria
DNA
Eukaryotes
RT
Archaea
Virus World
Cellular World
Genetic parasites
Self-contained
organisms
Viruses (including related mobile elements) and cellular life forms are the two
principal forms of biological organization
Virus particles (virions) are built of a
nucleic acid and a protein shell
Icosahedral (spherical) virions
Elongated (helical) virions
Virions under EM
Geminivirus (ssDNA within
a double sphere)
Tobacco mosaic virus
(ssRNA within a
helical rod)
Plant Virus Life Cycle
1
Invasion
Cytoplasm
Invasion through leaves:
vectoring insects;
mechanical damage
Invasion through roots:
vectoring nematodes or fungi;
mechanical damage
Exception: seed and pollen transmission
Virus Life Cycle
2
Genome uncoating, expression
and replication
uncoating
translation
replication
Cell
Wall
Virus Life Cycle
3
Particle (virion) assembly
Virus Life Cycle
4
Cell-to-cell movement
virions
Plasmodesma
CW
Virus Life Cycle
5
Systemic transport through phloem
Virus Life Cycle
6
Plant-to-plant transmission
..
RNA genome of TMV: ~6,400 nts,
three genes, and three major functions
RNA REPLICATION
RNA ENCAPSIDATION
CELL-TO-CELL MOVEMENT
beet soilborn
citrus mosaic (satsuma)
barley yellow dwarf
tomato spotted wilt (peanut)
tomato spotted wilt (tobacco)